The present invention relates to an improved process for the preparation of granular N-alkylammoniumacetonitrile salts of the formula I
R2R3N+R1xe2x80x94CR4R5xe2x80x94CN Yxe2x88x92xe2x80x83xe2x80x83(I)
in which
R1 is a C1- to C24-alkyl group, which can be interrupted by nonadjacent oxygen atoms or can carry additional hydroxyl groups, a C4- to C24-cycloalkyl group, a C7- to C24-alkaryl group or a group of the formula xe2x80x94CR4R5xe2x80x94CN,
R2 and R3 in each case independently of one another have the meaning of R1 or together are a saturated 4- to 9-membered ring having at least one carbon atom and at least one other heteroatom from the group consisting of oxygen, sulfur and nitrogen,
R4 and R5 in each case independently of one another are hydrogen, C1- to C24-alkyl groups, which can be interrupted by nonadjacent oxygen atoms or can additionally carry hydroxyl groups, C4- to C24-cycloalkyl groups or C7- to C24-alkaryl groups, and
Yxe2x88x92 is a sulfate or hydrogensulfate anion in the corresponding stoichiometric amount,
from an aqueous solution of the compound of the formula II
R2R3N+R1xe2x80x94CR4R5xe2x80x94CN R6Oxe2x80x94SO2xe2x80x94Oxe2x88x92xe2x80x83xe2x80x83(II)
in which R1 to R5 are as defined above and R6 is C1- to C4-alkyl.
N-alkylammoniumacetonitrile salts, such as N-methylmorpholiniumacetonitrile sulfate and hydrogensulfate are needed in particular as activators in the form of solids for low-temperature bleaching in detergents. WO 98/23531 describes granules of such compounds, which can additionally comprise carrier materials, for this application. For the preparation of such sulfate or hydrogensulfate granules, it is recommended to start from the methylsulfate salts.
However, known processes for the preparation of these solid N-alkylammoniumacetonitrile sulfates or hydrogensulfates are still in need of improvement. It is an object of the present invention to provide such a process which avoids the disadvantages of the prior art.
We have found that this object is achieved by the present process, which comprises evaporating the aqueous solution of the compound II at a temperature of from 80xc2x0 C. to 250xc2x0 C. and a pressure of from 100 mbar to 2 bar to give a melt, then allowing the melt to solidify, where, during or after the evaporation, customary carrier materials and/or auxiliaries can be added, and the resulting solidified compound I is converted into the desired granular form.
During the evaporation stage, water and also the corresponding C1- to C4-alcohol which becomes free upon the-partial or complete thermal hydrolysis of the counterion Y are removed from the aqueous solution of the compound II.
The radical R1, which has normally arisen as a result of the alkylation of the N atom, is, for example:
a straight-chain or branched relatively long or, in particular, relatively short alkyl radical having from 1 to 24 carbon atoms, where unsaturated radicals, in particular unsaturated fatty acid radicals are also suitable, e.g. methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, isononyl, decyl, undecyl, dodecyl, tridecyl, isotridecyl, myristyl, cetyl, stearyl or oleyl;
an alkoxyalkyl radical, e.g. methoxymethyl, 2-methoxyethyl, 3-methoxypropyl, 4-methoxybutyl, 2-ethoxyethyl or 3-ethoxypropyl;
a hydroxyalkyl radical, e.g. hydroxymethyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxy-2-butyl or 4-hydroxybutyl;
a radical constructed of repeating C2- to C4-alkylene oxide units such as ethylene oxide, propylene oxide or butylene oxide, which can be terminated by a hydroxyl group or an alkoxy group, e.g. (C2H4O)nxe2x80x94H or xe2x80x94(C2H4O)nxe2x80x94R7, xe2x80x94(C3H6O)mxe2x80x94H or xe2x80x94(C3H6O)mxe2x80x94R7, xe2x80x94(C4H8O)kxe2x80x94H or xe2x80x94(C4H8O)kxe2x80x94R7 n=2 to 11, m=2 to 7, k=2 to 5, R7=methyl or ethyl);
a cycloalkyl group such as cyclopentyl, cyclohexyl or cycloheptyl;
an aralkyl group such as benzyl, 2-phenylethyl, 3-phenylpropyl or 4-phenylbutyl;
a group of the formula xe2x80x94CH2xe2x80x94CN, xe2x80x94CH(CH3)xe2x80x94CN or xe2x80x94C(CH3)2CN.
Preferred meanings for R1 are a C1- to C4-alkyl group or a benzyl radical.
The meanings for the radicals R4 and R5 are in principle the same as for R1 (with the exception of xe2x80x94CR4R5xe2x80x94CN), and they can additionally also be hydrogen. Preferred meanings for R4 and R5 are hydrogen, methyl and ethyl, and in particular both are hydrogen.
In a preferred embodiment, R1 is a C1- to C4-alkyl group or a benzyl radical, and R4 and R5 are both hydrogen at the same time.
The meanings for the radicals R2 and R3 are principally the same as for R1 for open-chain alicyclic structures. Additionally, R2 and R3 can, together with the ammonium N atom, be a saturated heterocyclic ring. Suitable in particular in this connection are those which, apart from the ammonium N atom, contain no, one or two further heteroatoms from the group consisting of oxygen, sulfur and nitrogen, especially from the group consisting of oxygen and nitrogen. Preferred ring sizes are five-, six- and seven-membered rings. Examples of heterocyclic systems which are suitable for this purpose are imidazolidine, 1,2,3-triazolidine and piperazine.
Particular preference is given to systems in which R2 and R3 together are a saturated six-membered ring having 5 carbon atoms or having 4 carbon atoms and one oxygen or one nitrogen atom. These are in particular piperidine and morpholine systems.
The radical R6 is, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl, preferably methyl.
According to the process of the invention, very particular preference is given to preparing granular N-methylmorpholiniumacetonitrile hydrogensulfate from an aqueous solution of N-methylmorpholiniumacetonitrile methylsulfate.
Depending on the pressure, the evaporation is carried out at temperatures of from 80xc2x0 C. to 250xc2x0 C., preferably from 90xc2x0 C. to 200xc2x0 C., in particular at from 100xc2x0 C. to 160xc2x0 C. In the preferred pressure range, temperatures from 100xc2x0 C. to 160xc2x0 C. are particularly favorable because then adequate removal of water and alcohol takes place and the decomposition of the acetonitrile I to the corresponding amide stage is still negligibly slight.
The evaporation is carried out at a pressure of from 10 mbar to 2 bar, preferably from 100 mbar to 1.1 bar, in particular at from 250 to 960 mbar. Preference is given to evaporation under a slight vacuum since under these conditions volatile secondary components can be driven off more easily.
The evaporation step is preferably carried out in a continuous procedure, for example in a Sambay evaporator, a thin-film contact dryer, a falling-film evaporator or a tube-bundle heat exchanger. The evaporation can, however, also be carried out discontinuously, i.e. in a batch process, e.g. in a reactor.
The required residence time for the evaporation step is dependent on the temperature chosen and the pressure chosen and is generally in the range from a few minutes to several hours. A typical range is from 2 minutes to 15 hours, in particular from 5 minutes to 5 hours. In the preferred temperature and pressure range, a residence time of from 5 to 15 minutes is particularly favorable. Residence times which are too long can trigger the decomposition of the product. The residence time distribution should be narrow, in the case of a continuous procedure, the plugflow pattern should be strived for in order to avoid the formation of by products and decomposition products.
In a particularly preferred embodiment, the evaporation is carried out continuously with a residence time of from 5 to 15 minutes.
Leaving the evaporation stage are the product melt and vapors in the form of predominantly water and alcohol vapor. In the process according to the invention, the significant reduction in the input of energy can be achieved by using the condensation of the vapors produced during the evaporation to preheat the aqueous solution of the compound II. As regards apparatus, tube-bundle or plate-type heat exchangers can, for example, be used for this purpose.
The melts produced in this way usually have a water content of at most 30% by weight, in particular of at most 20% by weight, especially from 1 to 10% by weight. The proportion of the sulfate or hydrogensulfate salt I in the melt is usually at least 50% by weight, in particular at least 70% by weight, especially at least 80% by weight. The aqueous solution of the compound II used as starting material usually has a solids content of from 5 to 80% by weight, in particular from 10 to 75% by weight, especially from 25 to 65% by weight.
Prior to solidification, it is possible to mix the melt with customary carrier materials and/or auxiliaries. These carrier materials can be water-soluble or water-insoluble, depending on the field of application. Examples of such carrier materials, which are added during or after the evaporation, are sodium sulfate, silicas and zeolites. It is also possible to add two or more of said carrier materials, i.e. mixtures thereof. As well as carrier materials, functional auxiliaries such as surfactants can also be added to the melt.
The mixing with the carrier materials or auxiliaries can either be carried out in any separate apparatus, e.g. in a stirred vessel, or in a continuous mixer. The mixture can then be solidified by contact cooling, e.g. on a cooling roll, on a cooling belt or in a cooling mixer, or by convective cooling, e.g. in a prilling tower or in spray granulation equipment. It is, however, also possible to carry out the mixing and solidification of the melt in the same apparatus, e.g. in an extruder, kneader reactor or cooling mixer.
The cooling process can be carried out at superatmospheric pressure, atmospheric pressure or under reduced pressure. In principle, it is possible to operate here within the same pressure ranges as for the evaporation step. Preference is given in the case of the cooling process to carrying out the procedure under atmospheric pressure or, as in the case for the evaporation step, under slightly reduced pressure as a result of suction.
The cooling temperatures can be in the range from the solidification temperature of the melt to very negative temperatures, as, for example, is the case during cooling with liquid nitrogen (xe2x88x92196xc2x0 C.). Preference is given to cooling temperatures in the range from xe2x88x9250xc2x0 C. to +30xc2x0 C., in particular from xe2x88x9220xc2x0 C. to +20xc2x0 C.
The required residence time of the solidification process depends on the crystallization properties of the substance mixture and is generally in the range from a few minutes (e.g. 5 minutes) to one hour. Intimate thorough mixing, as occurs for example in extruders or kneader reactors, can considerably shorten the required crystallization time in many cases.
According to the solidification process, the product, which contains the salt I in addition to any remaining starting material II and optionally carrier materials and/or auxiliaries, is usually in the form of a solid with a broad particle size distribution and thus still does not satisfy, for example, the requirements for detergent granules. The desired granular form with respect to the particle size can be obtained by suitable screening and/or grinding steps with customary processing equipment. Customary particle sizes are from 100 to 5000 micrometers, in particular from 300 to 2000 micrometers.
The process according to the invention has a number of advantages. For example, it permits conversion with a low by product level and the reduction of volatile secondary components. The preferred continuous procedure results in high yields. Because the hold-up in the plant is short, the continuous procedure is advantageous for reasons of safety. The fact that it is possible to recover heat means that the process is energetically favorable. It is possible to use a very wide variety of carrier materials and auxiliaries in the granulation process. Furthermore, the particle size distribution in the granulation process can be readily controlled.